Electrostatic screen process printing with curved screens



Feb. 7, 1967 J. w. EDWARDS ELECTROSTATIC SCREEN PROCESS PRINTING WITH CURVED SCREENS 3 Sheets-Sheet 1 Filed July 19, 1965 FIG. 3

INVENTOR JAMES W. EDWARDS ATTORNEY Feb. 7, 1967 J. w. EDWARDS 3,302,561

ELECTROSTATIC SCREEN PROCESS PRINTING WITH CURVED SCREENS Filed July 19, 1965 5 Sheets-Sheet 2 FIG. 4

INVENTOR JAMES W. EDWARDS MM W ATTORNEY Feb. 7, 1967 J. w. EDWARDS ELECTROSTATIC SCREEN PROCESS PRINTING WITH CURVED SCREENS Filed July 19, 1965 3 SheetsSheet 5 IIII INVENTOR JAME S W. EDWARDS ATTORNEY United States Patent M 3,302,561 ELECTROSTATIC SCREEN PROCESS PRINTING WITH CURVED SCREENS James W. Edwards, Creve Coeur, Mo., assignor to Monsanto Company, St. Louis, Mo., a corporation of Delaware Filed July 19, 1965, Ser. No. 472,982 14 Claims. (Cl. 10138) This invention relates in general to certain new and useful improvements in electrostatic printing, and more particularly, to an improved method and apparatus for electrostatically printing on curvilinearly shaped articles.

Since the :advent of the thin-walled disposable containers made of plastic and synthetic resinous materials, these containers have found widespread use in the packaging industry. The vending machine industry particularly has been employing large quantities of nestable plastic containers in addition to the long-used conventional nestable paperboard containers. It is generally necessary, in this type of industry, to imprint the contents of the container, the name of the manufacturer, and/or distributor, and any other advertising identification material on the side wall of the container. The conventional printing methods employing offset printing techniques were not generally acceptable because they were not adapted to massiproduction operation and did not produce a desired quality of print. Because of the low profit margin on disposable containers, profits in this type of field are generally made on a volume sale basis. Accordingly, it is necessary to print containers of this type in an economically feasible manner and the containers must be printed automatically by suitable apparatus.

In an effort to find a suitable method of imprinting containers having frustro-conical shapes, there have been certain investigations in the field of electrostatic printing. However, the art of electrostatic printing is relatively new and this particular type of printing was only available for printing on fiat or relatively flat items. To date, electrostatic printing techniques have not been adaptable for use in printing relatively large areas on nonpl'anar surfaces.

The presently known techniques in electrostatic printing are described in United States Letters Patent No. 3,081,698 which relates to a method of electrostatic printing by elimination of pressure or contact between the printing element and the subject material being printed. This technique involves the transfer of a liquid based ink or a resinous based ink through an electrostatic field to an image-receiving object. The ink or pigments are usually in the form of .a fine powder having a particle size which is small enough to pass through the interstices of the open areas of a stencil or so-called screen. A roller or similar mechanical device normally carries the ink particles to a point in close proximity to the stencil and where the ink is carried through the stencil by the electrostatic field to the image-receiving object. During the transfer, the ink particles are triboelectrically charged and are thus attracted toward the image receiving object by an electrical potential applied to the object or to the backing electrode. The charge of the particles is, of course, opposite to the backing plate and the ink particles are, therefore, accelerated through the openings or interstices in the open areas of the screen and toward the image-receiving object. The image-receiving object may consist of a mandrel which serves as a counter-electrode and which is capable of retaining the article to be printed. Thereafter, the pigment will collide with and adhere to the article which is to be printed and the image is subsequently fixed by heat or solvent or a vapor or by other suitable means which are known in the prior art.

" appearance of the printed image.

3,392,561 Patented Feb. 7, 19567 Since the initial development of the theory of electrostatic printing, there have been many attempts to produce devices which are capable of automatic printing. Moreover, there have been attempts to print non-linearly shaped articles by electrostatic methods. However, all of the attempts to produce these automatic and semi-automatic devices for electrostatic printing have been rather unsuccessful and commercially unfeasible for a number of reasons. All of the electrostatic printing devices thus far employed have involved the transfer of ink across a definite and appreciable space and the particles of ink had to be physically transported across this space.

The devices heretofore available for electrostatic printing were not successfully adaptable for use in electrostatically printing curvilinearly shaped articles such as frustro-conically shaped containers. Curvilinearly shaped articles presented an unusual problem in electrostatic printing due to the fact that each portion of the article to receive electroscopic ink did not lie within the same plane as the ink receiving plane of the electrostatic screen. Consequently, there was a variable distance between the ink receiving media and the electrostatic screen when attempting to print curvilinearly shaped articles. For this reason, attempts to electrostatically print on conically shaped containers such as disposable drinking cups presented particularly difficult problems to overcome. Due to the fact that the ink receiving surface of the comically shaped cup did not lie within the same horizontal plane as every portion of the screen surface, ink delivery was uneven. The printing on these devices suffered areas of reduced color density as a result of uneven ink distribution. These areas of reduced color density have an outline of a printed pattern often referred to as ghosting or memory effect" and materially reduces the aesthetic Moreover, due to the fact that each portion of the ink receiving member did not lie within the same plane, parallel to the plane of the screen, some ink particles had to traverse a greater distance in the electrostatic field and hence the ultimate image produced was distorted, uneven and smeared.

It is, therefore, the primary object of the present invention to provide electrostatic printing apparatus which are capable of electrostatically printing a large variety of articles having varying sizes and curvilinear shapes.

It is another object of the present invention to provide an electrostatic printing apparatus of the type stated which is adaptable for use in mass-production methods of electrostatic printing and does not require employment of especially designed electrodes or devices for altering electrostatic fields.

It is a further object of the present invention to provide a method of electrostatically printing curvilinearly shaped articles which requires a minimum amount of manual attention.

It is an additional object of the present invention to provide electrostatic printing apparatus of the type stated which employs an electrostatic printing screen having about the same shape and surface contour as the article to be printed.

It is also an object of the present invention to provide an electrostatic printing apparatus of the type stated which is capable of convenient modification for electrostatic printing on any type of curvilinear article.

It is another salient object of the present invention to provide an electrostatic printing apparatus and method of the type stated which provides a technique for electrostatic printing on curved surfaces without smearing or creating ghosting effects.

With the above and other objects in view, my invention resides in the novel features of form, construction,

=3 arrangement and combination of parts presently described and pointed out.

In the accompanying drawings (3 sheets):

FIGURE 1 is a schematic perspective view, partially broken away, of an electrostatic printing apparatus constructured in accordance with and embodying the present invention;

FIGURE 2 is a vertical sectional view taken along line 22 of FIGURE 1 and showing the spacial relationship of the various components forming part of the electrostatic printing apparatus of FIGURE 1;

FIGURE 3 is an exploded perspective view, partially broken away, of the electrostatic printing apparatus of FIGURE 1 showing a mandrel forming a part of the invention partially withdrawn from the electrostatic printin-g screen;

FIGURE 4 is a vertical sectional view taken along line 44 of FIGURE 3;

FIGURE 5 is a vertical sectional view, partially broken away, and showing end elevation of the electrostatic printing apparatus of FIGURE 1 with the interposition of a mask between the screen and feeding roller forming part of the invention;

FIGURE 6 is a vertical sectional view, partially broken away, of a modified form of electrostatic printing apparatus constructed in accordance with and embodying the present invention; and

FIGURE 7 is a vertical sectional view similar to the sectional view of FIGURE 6 showing the printing apparatus of FIGURE 6 with the mandrel forming a part thereof in an extended position.

The art of electrostatic printing is still a recent technological innovation, and the terminology peculiar to this technology has not yet achieved a commonly acceptable and understood usage and definition. Accordingly, the term printing as used herein, is employed to describe the operation of a delivery ink from the ink member to the element being printed, although it is to be understood that the word printing as used herein does not connote any mechanical pressure. The word printing is used in its much broader sense of the word merely to mean transfer of a design from one element to another in analogous form to the use of the term printing in photography Where mechanical pressure is not the cause of transference of the design. In interpretation of the specification and the following claims, all terminology borrowed from the conventional printing art must, therefore, be given a broad meaning appropriate to this specialized field of electrostatic printing.

Generally speaking, the apparatus of the present invention is designed for use in mass-production electrostatic printing systems similar to the type described in copending application Serial No. 463,109 filed June 11, 1965. An electrostatic printing system of the type with which the present apparatus can be employed contains an electrically charged mandrel or counter-electrode and an electrically charged screen, the latter having a suitably imprinted pattern for creating the desired printed image. The stencil or screen generally comprises a fine mesh element of conductive material having masked non-printing areas. The ink particles are sized to pass through the interstices of the non-masked printing areas and carried by an electrostatic field to the mandrel or counter-electrode and thereby deposited on the article which is retained on the mandrel or counter-electrode.

The apparatus of the present invention provides for electrostatic deposition of electroscopic ink on surfaces having conical or cylindrical shapes. The apparatus generally comprises a mandrel which has a size, shape and surface contour adapted to receive a suitable article so that the latter can be retained on the mandrel. The article is generally a conically shaped container such as the commercially available thin-walled disposable plastic drinking cup. The apparatus of the present invention also provides an electrostatic printing screen which is designed to surround the article that is retained on the mandrel and generally fits over the article on the mandrel. The screen is slightly spaced from the container so that ink passing through the screen will be carried by an electrostatic field maintained in the space between the screen and container. The screen and container simultaneously rotate with respect to the feeding apparatus so that ink is deposited on the open mesh portions of the screen as it passes beneath an ink delivery means. The ink is thereafter carried by the electrostatic field to the container where it is deposited on the surface or side wall of the container.

The mandrel is adapted to be withdrawn from the screen so that the container may be ultimately removed and a new container inserted thereon. The electroscopic ink which adheres to the surface of the container is subsequently fixed by heat or solvent or a vapor or other suitable means available for fixing electroscopic inks.

A modified form of electrostatic printing apparatus forming part of the present invention is also provided Where a mandrel designed to contain an article to be printed is shifted into an electrostatic printing screen which is completely surrounded by a novel type of ink feeding mechanism. This mechanism generally comprises a housing which surrounds the screen and is at least partially filled with inert ink dispersing particles. Ink is slow ly metered into the housing and will accumulate among the spaces between the various ink dispersant particles. When the mandrel is shifted inwardly into the screen, a suitable mechanism is provided for jarring the housing at the same time the electrostatic field is completed. By simple jarring of the housing, the ink particles will be propelled towards the electrostatic screen and through the screen toward the mandrel by the electrostatic field.

Referring now in more detail and by reference characters to the drawings which illustrate practical embodiments of the present invention, A designates an electrostatic printing apparatus generally comprising a truncated, conically shaped electrostatic printing screen 1 having an annular tapering side wall 2 and which is provided with supporting rings 3 at each of its transverse ends. The side wall 2 is provided with a non-masked printing area 4 having a suitably imprinted image which is designed for transference to an article, ultimately to be printed. By reference to FIGURE 1, it can be seen that the image 4 is formed by a non-masked area where the remainder of the side wall 2 is substantially solid and impervious to the passage of electroscopic ink. The electrostatic screen 1 is provided with an open end 5 and an end wall 6 at the opposite end, the end wall 6 containing a hub 7 for mounting on a screen supporting shaft 8. The screen supporting shaft is connected to a suitable mechanism (not shown) for rotating the screen 1.

It is not necessary to have regularity of openings of a fine mesh screen or sensitized net in the electrostatic printing screen 1. The regular openings in fibrous material and the like can be satisfactory for purposes of the screen 1 as long as the openings and the particle size of the pigment are compatible for movement therethrough. The electrostatic printing screen 1 of the present invention is preferably made by the method set forth in copending application Serial No. 473,013, filed July 19, 1965. The electrostatic printing screen 1 is generally formed of a wire mesh metal fabric which is suitably provided with a photosensitive emulsion on one surface thereof. Thereafter, the photosensitive emulsion is exposed to a suitable source of light through a negative having the desired image. The portion of the photosensitive emulsion which is exposed to light becomes hardened and the remainder, which has not been exposed to light is then washed off in a hardening bath, generally a bath of hot water. In this case, the negative employed is actually a positive so that the image area receives a hardened emulsion. Thereafter, the screen is formed into a desired shape. For the purposes of the present invention, the screen is formed into a truncated conically shaped element. The screen is there after dipped into a slurry of metal powder permitting metal to fill the interstices of the open meshed portions which do not lie in the image area. The metal particles are then compacted in a suitable pressure apparatus and sintered in a conventional sintering furnace. In the sintering operation, the photosensitive emulsion which resides in the image area disintegrates and the image area, therefore, has open mesh portions while the remaining portions of the screen will be impervious to the passage of electroscopic ink. This type of process enables the production of a rigid self-supporting screen.

The electrostatic printing screen 1 may also be made in the method described in copending application Serial No. 463,251, filed June 11, 1965. In this process, a direct screen photosensitive emulsion is applied to a wire mesh metal fabric held in a screen chase. The screen is then exposed to light through a photographic negative of the required print or design which is ultimately to be produced on a substrate. The wire mesh is thereafter washed for removal of the unexposed emulsion, thereby leaving a positive image on the screen. The positive image is thereafter converted to a negative image required for printing by an electroplating operation. The electroplating creates a plating preferentially to the open mesh portions of the wire mesh. The screen is thereafter subjected to an emulsion remover where the emulsion remover clears the printing areas thereby leaving a negative screen in which the non-printing areas have interstices filled with metal. The metallized screen is then formable to a desired shape by rolling, drawing or any other conventional metal forming process.

The apparatus A of the present invention also includes a mandrel 9, which is coaxially mounted with respect to the screen 1 and is axially shiftable with respect to the screen 1 in the manner as shown in FIGURES 1 and 3. The mandrel 9 is also truncated and conically shaped and has an overall shape and surface contour which is substantially similar to the surface contour of the electrostatic printing screen 1. However, the mandrel 9 is slightly diametrally smaller than the screen 1 so that the mandrel 9 can be removably inserted into the open end 5. Thus, it can be seen that the mandrel 9 is axially shiftable into printing position, that is the position as shown in FIGURE 1 and to a loading position, that is the position shown in FIGURE 3. In actuality, the mandrel 9 is completely removable from the screen 1 so that a container C disposed thereon can be removed from the mandrel and another container C reinserted on the mandrel 9.

The mandrel 9 is provided with a flat end Wall 10 having an integrally formed hub 11 for supporting a mandrel shaft 12. The shaft 12 is connected to a suitable prime mover (not shown) for rotating the mandrel 9 in timed relation to the rotation of the screen 1. The prime mover for rotation of the mandrel 9 may be the same prime mover as employed for rotation of the screen 1. However, it should be understood that the screen 1 and the mandrel 9 rotate so that there is no relative movement therebetween. In other words, the mandrel 9 and the screen 1 must have the same angular speed, but not necessarily the same peripheral speed. Furthermore, it should be understood that the mandrel 9 has a surface contour and size which is designed to conform approximately to the article which is to be disposed thereon. In the present invention, the mandrel is illustrated and described as having a frustro-conical shape so that it is capable of receiving thin-walled disposable plastic drinking containers of the type described in United States Letters Patent No. 3,139,213.

The mechanism for shifting the mandrel 9 axially with respect to the screen 1 is conventional in its construction and is, therefore, neither illustrated nor described in de- 6 tail herein. It should also be noted that the screen 1 is provided in the end wall 6 with a plurality of air holes or air apertures 13.

Mounted in close proximity to the screen 1 for applying electroscopic ink thereto is an ink feeding mechanism 14 which is similar to the ink feeding mechanism described in 'copending application Ser. No. 453,706, filed May 6, 1965, and generally comprises an ink feeding roller 15 which is rotatably mounted on a supporting shaft 16. The inking roller or feeding roller 15 is provided on its annular surface with a pile fabric material 17, the latter of which resides in facewise contact with the side wall 2 of the screen 1. The fabric 17 may be secured to the roller 15 by any suitable adhesive and is preferably of a relatively thick bristle-brush construction, such as a mohair pile fabric. It has also been found that when the fabric 17 is formed of a foamed elastomer material, very effective results have been obtained. The fabric 17 is not necessarily limited to the above materials inasmuch as the important criterion in selection of the fabric 17 is that the material must have a sufiicient number of cavities or interstices into which ink powder can be deposited and subsequently transferred to the screen 1. The fabric 17 must also have a different triboelectric charging potential than the ink which is selected for use in the printing operation.

The inking or feeding roller 15 also serves as an electrode and establishes an electrostatic field between the mandrel 9 which serves as the counter-electrode and the inking roller 15. The electrostatic field between the mandrel 9 and the feeding roller 15 is developed by a variable high potential source as illustrated in FIGURE 2. This source is adapted to develop a relatively high direct current potential. While the current requirements for electric printing of the type herein employed are not heavy in the ordinary sense, a very definite electron current or space current flows across the printing space during the printing operation. It is desirable to have a space current of at least 1 to 2 milliamperes per square inch of printing area. Moreover, the high potential source should be capable of maintaining a desired voltage under current drains in the range of approximately milliamperes or slightly more.

Operatively mounted in contact with the fabric 17 of the roller 15 is a distributor roller 18 having a fabric surface 19, the latter of which is similar to the fabric surface 17 and may be formed of identical material. The roller 18 is rotatably mounted on a shaft 20, which is parallel in space to the shaft 16. The roller 18 is disposed beneath and in contact with the discharge outlet 21 of an ink hopper 22, all as can best be seen in FIGURE 1. The bristles of the fabric 19 are sized to extend into the slot forming part of the discharge outlet 21 and thereby act as an effective sealing means for the hopper 22. Thus as the roller 18 rotates, it will pick up selected quantities of ink and transfer the ink to the feeding roller 15, which will, in turn, transfer the ink to the screen 1. The hopper 21 may be formed of any suitable synthetic resin or plastic material or of any material which is inert with respect to the ink.

Any of a variety of electroscopic inks can be employed in the present invention. Generally, the electroscopic inks comprise a finely dispersed powder which is capable of being triboelectrically charged. The powder generally carries desired pigments or dyes. A number of satisfactory powders can be employed in the present invention and each must be in a finely divided state. Suitable powders are dyed thermoadhesive resins such as rosin, gum copal, gum sandarac, ethyl cellulose, Egyptian asphalt, various synthetic resins and the like. A very satisfactory thermoadhesive powder can be produced by dissolving equal parts of ethyl cellulose and Vinsol resin in acetone together with a small amount of spirit soluble aniline dye such as Nigrosine or aniline blue and spray drying the solution to produce an extremely fine powder having substantially spherical particles. Dyed lycopodium powder is suitable where thermoadhesive properties are not required of the power, as is also starch, cellulose flour, powdered metal and copper powder.

The electroscopic ink is maintained in a fluidized state or so-called fluid state and may be fluidized by any conventional process such as passing low pressure air through a porous membrane on which the ink particles are maintained in combination with a vibratory action. The ink contained within the hopper 22 must, therefore, be maintained in the fluidized state. For this purpose, the hopper 22 is generally provided with some suitable agitator means for keeping the ink particles in a suspended or levitated state.

Either fusible, thermoadhesive or non-fusible powders or others are used. The particle size is preferably near the limit of definition of the eye under ordinary reading conditions. Excessive powder size contributes to graininess in appearance of the image. On the other hand, extremely fine powder may be undesirable in many instances due to its tendency to ball up or cling together in clusters. It is, therefore, desirable to use a powder in which substantially all the particles are Within the size range from 0.5 to 25 microns. If spherical powders are used, this refers to their diameters, otherwise to the largest dimension. For most purposes, it is preferred to use an equidimensional powder particle, the sphere being the preferred form.

By further reference to FIGURES 1 and 3, it can be seen that the fabric 19 on the distributor roller 18 picks up ink from the hopper 22 as it rotates slowly and transfers the ink particles to the fabric 17 on the rapidly turning feeding roller 15. The rubbing action between the rollers 15 and 18 produces electrical charges on the ink particles. An additional roller (not shown) is employed for triboelectrically charging the particles when printing large area images. This roller is of similar construction to rollers 15 and 18 and operates in tangential contact with the roller 15. This roller contributes to the triboelectric charging of the ink and, most importantly, redistributes the ink carried on the roller 15 and thereby eliminates ghosting effects. The particles, however, can be charged in any conventional manner as may be desired or by any suitable means of triboelectric charging. Moreover, the particles can be charged by means of a corona discharge. The ink particles which are then transferred to the feeding roller 15 are passed to the screen 1 where they are suspended in the electrostatic field and transferred to the container C by the propelling force of the electrostatic field.

The screen 1 and the mandrel 9 are designed to rotate in timed relationship to the rotation of the feeding roller 15. By reference to FIGURES 1 and 3, it can be seen that the feeding roller 15 is so located that tangential contact is made along a line parallel to the axis of rotation of the roller 15 and parallel to the surface of the screen 1. Thus, it can be seen that while the axis of rotation of the rollers 15, 18, namely the shafts 16, 20 respectively, are parallel in space, they are not parallel in space to the shafts 12 or 8, which provide the axis of rotation of the screen 1 and the mandrel 9, respectively. However, it should be observed that the shaft 6 is coplanar to the shafts 8, 12. The shaft 20 does not necessarily have to be coplanar to the shafts 8 and 12. As previously indicated, the mandrel 9 and the screen 1 are designed to rotate at the same angular speed so that there is no relative movement between the mandrel 9 and the screen 1. The roller 15 is designed to rotate at a different peripheral speed from the screen 1 so that a continuing line of tangential brushing contact is maintained between the surface of the fabric material 17 and the side wall 2 f the screen 1. In this manner, ink is transferred from the feeding roller through the line of tangential contact to the screen 1 and through the image pattern 4 to the passed beneath the roller 15. The ink supply which is continually passed through the image pattern 4 is then deposited on the container C, Where it adheres thereto until a final fixing of the electroscopic ink. After the entire image pattern 4 has passed beneath the roller 15, the mandrel 9 and the container C disposed thereon is withdrawn from the conically shaped screen 1. A new container C is disposed on the mandrel 9. While the operation of loading a new container C on the mandrel 9 is proceeding, the polarity of the electric field between the screen 1 and feed roller 15 is reversed. This will cause the ink previously deposited on the closed portions of the screen to return to the feed roller, thus preventing heavy-edge effects in the printed image. The mandrel 9 is then returned and the printing operation is repeated, thereby starting a new printing cycle. Moreover, it should be observed that the screen 1 and the mandrel 9 are shiftable away from the feeding roller 15 during the nonprinting portion of the cycle, substantially as shown in FIGURE 4. In addition, by suitable apparatus, the ink feeding mechanism can be intermittently stopped during the non-printing portions of the cycle.

It should be recognized that the above invention has been described in terms of printing on conically shaped containers. For this purpose, the screen had a truncated conically shaped section, as did the mandrel and the container. It can be observed from FIGURES l and 2 that the mandrel was slightly smaller than the container and the container was slightly smaller than the screen so that the container was interposed between the mandrel and the screen. It should, however, be recognized that it is possible to use the same type of apparatus for printing on other articles having curvilinear shapes. For example, printing can be performed on cylindrically shaped objects or on hyperbolically shaped objects. The only important criterion for the purpose of the present invention is that the article must be capable of insertion into a screen having a similar shape and surface contour. It should also be recognized that the mandrel of the present invention can be eliminated and any suitable supporting device designed to retain the article to be printed may he substituted for the mandrel. However, it must also be understood that the supporting device should have an axis of rotation which is coaxial with respect to the axis of rotation of the screen.

As illustrated in FIGURE 5, if desired, a conventional mask consisting of two web-shaped elements may be interposed between the roller 15 and the mandrel 1. The mask often assists in eliminating any potential ghosting problems.

It is possible to provide a modified form of electrostatic printing apparatus B substantially as shown in FIG- URES 6 and 7. The electrostatic printing apparatus B generally comprises an electrostatic printing screen 25 which is substantially similar to the previously described printing screen 1 and has a side wall 26 with a desired printing image 27 formed thereon. The screen 25 is provided with solid non-printing areas and open mesh printing areas such as in the area 27. The screen 25 is also provided with a substantially solid top wall 28. The screen 1 is provided with a bottom supporting ring 29 for securement to an electroscopic ink-containing housing 30. The screen 25 may be constructed in the manner as previously set forth in connection with the construction of the screen 1. The housing 30 is formed with an annular side wall 31, a bottom wall 32 and a top wall 33, substantially as shown in FIGURE 6. Thus, it can be seen that the housing 30 is formed about the screen 25 and surrounds the screen 25. Moreover, it can be seen that the screen 25 extends upwardly into the housing 30 for the greater portion of its overall height.

The housing 30 is packed, at least to the top wall 28 of the screen 25, with suitable ink dispersant beads forming a packing 34. The beads may be formed of any material which is inert with respect to the electroscopic ink,

such as any of a number of ceramic materials, i.e. glass, quartz, various synthetic resins, and composites, etc. The particles may have any shape but are preferably round and should be within the overall size of approximately 0.020 to 0.100". The housing 30 is also formed of a material which is inert with respect to the ink and may be formed of any of the materials selected for use in construction of the ink hopper 22.

Mounted above the housing 30 is an ink hopper 35 for supplying eleectroscopic ink to the housing 30. Again, the hopper 35 is substantially similar in its construction to the ink hopper 22 and is formed of the same material of construction as the hopper 22. Additionally, the ink hopper 35 is preferably provided with an agitator for maintaining the electroscopic ink in a levitated or suspended state. The hopper 35 is mounted above the housing 30 and is stationary with respect to the housing 30. The hopper 35 is provided with a series of discharge chutes 36 which communicate with the interior of the housing 30 and permit metering of electroscopic ink into the housing 39 at a uniform rate. Preferably, the hopper 35 should be provided with means( not shown) for metering the electroscopic ink distribution to the housing 30. Additionally, the hopper 35 may be provided with a mechanism for optionally discontinuing the flow of ink to the housing 30. Again, it should be understood that any of the inks which were employed in connection with the electrostatic printing apparatus A may also be adopted for use in the electrostatic printing apparatus B.

Some of the ink which is disposed in the housing 30 may not be shifted toward the electrostatic printing screen 25 and may not be employed in an electrostatic printing operation. In order to prevent an excess accumulation of electroscopic ink in the housing 31, a pair of discharge chutes 37 are operatively connected to the underside of the housing 30 and lead to an ink collecting trough 38. The discharge chute 37 may have a screen interposed in its pathway or other means for preventing removal of any of the packing 34 or other control means (not shown) for regulating the amount of ink which is withdrawn from the housing 30. It should be understood that the ink which is collected in the trough 38, can be recirculated and again deposited in the hopper 35, after sufficient accumulation has been collected in the trough 38.

Provided for vertically shiftable movement into and out of a pocket or chamber 39, formed by the screen 25, is a mandrel 46 for supporting the container C. Again, it should be recognized by reference to FIGURE 6, that the container C, the mandrel 40 and the screen 25 have similar shape and surface contour. However, the screen 25 is slightly larger than the container C and the container C is slightly larger than the mandrel 40. The mandrel 40 is operatively secured to a mandrel supporting shaft 41, which is in turn connected to a suitable mechanism (not shown) for vertically shifting the mandrel 40 into-the pocket 39. This latter mechanism is conventional in its construction and does not in and of itself form the present invention. It is, therefore, neither illustrated nor described in detail herein.

Also mounted on the mandrel supporting shaft 41 is an outwardly extending arm 42 with an upwardly extending plate 43 designed to abut against the bottom wall 32 of the housing 30 and slightly jar the housing 30 when the mandrel 40 is shifted to the position as shown in FIGURE 6. A suitable mechanism is also provided for introducing the current necessary to create the electrostatic field between the screen 25 and the mandrel 40 when the mandrel 40 is shifted to the printing position, that is the position as shown in FIGURE 6. Simultaneously with the initiation of the electrostatic field, the plate 43 will momentarily abut against the bottom wall 32 and thereby jar the housing 30. As the plate 43 jars the housing 30, the electroscopic ink contained among the various particles of the packing 34 will also become jarred and shifted slightly. At this point, the introduction of the electrostatic field will move the ink particles toward the screen 25 and through the printing image 27 to the container C on the mandrel 40. The electroscopic ink particles will then become deposited on the container C.

Thus, it can be seen that neither the mandrel 40 nor housing 30 is designed for movement with respect to the other. The only movement necessary is the shifting of the mandrel 40 into the chamber 39. It should also he observed that the mandrel could be lowered into the chamber 39. In other words, the screen would open upwardly and the man-drel shift vertically downward into the chamber 39. It should also be recognized that any suitable means for instantaneously jarring the housing 30 at the time the mandrel 40 is shifted therein may be employed and the present invention is not limited to the plate 43 which abuts against the bottom wall 32.

It should be understood that changes and modifications may be made in the form, construction, arrangement and combination of parts presently described and pointed out without departing from the nature and principle of my invention.

Having thus described my invention, what I desire to claim and secure by Letters Patent is:

1. An apparatus for electrostatically printing articles having a curvilinear shape, said apparatus comprising a screen having a circumferentially closed and continuous surface of revolution with a surface contour substantially similar to the article to be printed, supporting means coaxially positioned with respect to said screen for holding the article in spaced relation to the screen, means for coaxially shifting said supporting means into and out of the continuous surface of revolution of said screen, ink supply means for feeding electroscopic ink to said screen, and means for establishing an electrostatic field between said supporting means and screen so that ink will flow through the open mesh portions of said screen to the article and thereby transfer the image pattern on said screen to the article.

2. An apparatus for electrostatically printing articles having a curvilinear shape, said apparatus comprising a screen having a surface contour substantially similar to the article to be printed, said screen having a circumferentially closed and continuous surface of revolution forming an interior chamber, the surface of revolution of said screen 'being slightly diametrally larger than the diametral size of the surface of revolution of said article so that no contact exists therebetween, supporting means for retaining the article and positioning the article in the interior chamber said supporting means having an axial centerline which is coincident with the axial centerline of the surface of revolution of said screen, means for coaxially shifting the supporting means into and out of the chamber along said axial centerline so that the article is concentrically positioned in the screen and is equidistantly spaced from the screen at all points, ink supply means for feeding electroscopic ink to said screen, and means for establishing an electrostatic field between said supporting means and screen so that ink will flow through the open mesh portions of said screen to the article and thereby transfer the image pattern on said screen to the article.

3. The process of electrostatically printing on articles having a curvilinear shape with a screen having a circumferentially closed and continuous surface of revolution and where-in the screen has a surface contour and shape substantially similar to the article; said method comprising coaxially shifting the article into the surface of revolution along a line which is coincident with the axial centerline of the surface of revolution, positioning the article in the surface of revolution so that all points on the article are equidistant from all opposed points on the screen, establishing an electrostatic field between the screen and article, feeding electroscopic ink from a feeding mechanism through open mesh portions of the screen by the force of the electrostatic field and to the article, rotating the screen and article with respect to the feeding mechanism but at a peripheral speed so that there is no relative movement between the screen and article, and coaxially withdrawing said article from said surface of revolution so that the axial centerline of the article is coincident with the axial centerline of the surface of revolution.

4. The process of electrostatically printing on articles having a curvilinear shape with a screen having a circumferentially closed and continuous surface of revolution and wherein the screen has a surface contour and shape substantially similar to the article; said method comprising coaxially shifting the article into the surface of revolution along a line which is coincident with the axial centerline of the surface of revolution, positioning the article in the surface of revolution so that all points on the article are equidistant from all opposed points on the screen, establishing an electrostatic field between the screen and article, feeding electroscopic ink from an ink feeding roller through open mesh portions of the screen by the force of the electrostatic field and to the article, positioning the feeding roller so that it has a line on its surface parallel in space to a line on the surface of the screen, rotating the screen and roller so that instantaneous tangential contact is made between the screen and article, whereby ink will pass through the screen at the line of tangential contact to the container, and coaxially withdrawing said article from said surface of revolution so that the axial centerline of the article is coincident with the axial centerline of the surface of revolution.

5. The process of electrostatically printing on articles having a curvilinear shape with a screen having a circumferentially closed and continuous surface of revolution and wherein the screen has a surface contour and shape substantially similar to the article; said method comprising coaxially shifting the article into the surface of revolution along a line which is coincident with the axial centerline of the surface of revolution, positioning the article in the surface of revolution so that all points on the article are equidistant from all opposed points on the screen, establishing an electrostatic field between the screen and article, feeding electroscopic ink from an ink feeding roller through open mesh portions of the screen by the force of the electrostatic field and to the article, positioning the feeding roller so that it has a line on its surface parallel in space to a line on the surface of the screen, rotating the screen and article with respect to the feeding roller but at an angular speed so that there is no relative movement between the screen article, and rotating the screen and roller so that instantaneous tangential contact is made between the screen and article, whereby ink will pass through the screen at the line of tangential contact to the container, and coaxially withdrawing said article from said surface of revolution so that the axial centerline of the article is coincident with the axial centerline of the surface of revolution.

6. The process of electrostatically printing on articles having a curvilinear shape with a screen having a circumferentially closed and continuous surface of revolution and wherein the screen has a surface contour and shape substantially similar to the article; said method comprising positioning the screen internally in an ink feeding container, depositing ink particles among inert particles in said ink feeding container, axially shifting the article in the surface of revolution of said screen so that the axial centerline of the screen is coincident with the axial centerline of the article, establishing an electrostatic field between the screen and article and simultaneously and momentarily jarring the ink feeding container, and feeding electroscopic ink through open mesh portions of the screen by the force of the electrostatic field and to the article thereby transferring the image pattern on said screen to the article.

7. An apparatus for electrostatically printing conically shaped articles having an axial centerline and a frustoconical side wall, said apparatus comprising a screen having an axial centerline and a frustoconical side wall with a surface contour substantially similar to the article to be printed, the side wall of said screen having a surface of revolution forming an interior chamber, the surface of revolution of said screen being slightly diametrally larger than the diametral size of the surface of revolution of said article so that no contact exists therebetween, supporting means for retaining the article and positioning the article in the interior chamber, said supporting means having an axial centerline which is coincident with the axial centerline of the surface of revolution of said screen, means for coaxially shifting the supporting means into and out of the chamber along said axial centerline so that the article is concentrically positioned in the screen and is equidistantly spaced from the screen at all points, ink supply means for feeding electroscopic ink to said screen, and means for establishing an electrostatic field between said supporting means and screen so that ink will flow through the open mesh portions of said screen to the article and thereby transfer the image pattern on said screen to the article.

8. An apparatus for electrostatically printing articles having a curvilinear shape, said apparatus comprising a screen having a surface contour substantially similar to the article to be printed, said screen having at least one surface of revolution forming an interior chamber, the surface of revolution of said screen being slightly diametrally larger than the diametral size of the surface of revolution of said article so that no contact exists therebetween, supporting means for retaining the article and positioning the article in the interior chamber said supporting means having an axial centerline which is coincident with the axial centerline of the surface of revolution of said screen, means for coaxially shifting the supporting means into and out of the chamber along said axial centerline so that the article is concentrically positioned in the screen and is equidistantly spaced from the screen at all points, ink supply means for feeding electroscopic ink to said screen, means for establishing an electrostatic field between said supporting means and screen so that ink will flow through the open mesh portions of said screen to the article and thereby transfer the image pattern on said screen to the article, and means associated with said last named means for initiating the electrostatic field when the article is positioned in the chamber and removing the electrostatic field when the article is removed from the chamber.

9. An apparatus for electrostatically printing articles having a curvilinear shape with a surface of revolution, said apparatus com-prising a screen having a surface of revolution with a contour substantially similar to the article to be printed, said screen having a surface of revolution which is slightly diametrally larger than the diametral size of the surface of revolution of said article so that no contact exists therebetween, supporting means for axially shifting the article into said screen and holding the article in the surface of revolution of and in spaced relation to the screen, said supporting means having an axial centerline which is coincident with the axial centerline of the surface of revolution of said screen, ink supply means including an ink delivery roller in proximate relation to the screen for feeding electroscopic ink to said screen, means for moving the supporting means and screen with respect to said ink supply means but at such speeds so there is no relative movement between said supporting means and screen, means for positioning and rotating said delivery roller so that tangential approach and departure is maintained between said screen and said feeding roller, and means for establishing an electrostatic field between said supporting means and screen so that ink will flow through the open mesh portions of said screen to the article and thereby transfer the image pattern on said screen to the article.

10. The apparatus of claim 9 where both the screen and the article are conically shaped.

11. An apparatus for electrostatically printing articles having a curvilinear shape with a surface of revolution, said apparatus comprising a screen having a surface of revolution with a contour substantially similar to the article to be printed, said screen having a surface of revolution which is slightly diametraliy larger than the diametral size of the surface of revolution of said article so that no contact exists therebetween, supporting means for axially shifting the article into said screen and holding the article in the surface of revolution of and in spaced relation to the screen, said supporting means having an axial centerline which is coincident with the axial centerline of the surface of revolution of said screen, an ink delivery roller in proximate relation to the screen for feeding electroscopic ink to said screen, ink supply means operatively associated with said ink delivery roller for supplying electroscopic ink thereto, an ink distributor roller operatively interposed between said ink delivery roller and said ink supply means for depositing ink from said supply means on said delivery roller and providing a triboelectric charge to the ink particles, means for moving the supporting means and screen with respect to said ink delivery roller but at such speeds so there is no relative movement between said supporting means and screen, means for positioning and rotating said delivery roller so that tangential approach and departure is maintained be tween said screen and said feeding roller, and means for establishing an electrostatic field between said supporting means and screen so that ink will flow through the open mesh portions of said screen to the article and thereby transfer the image pattern on said screen to the article.

12. An apparatus for electrostatically printing articles having a curvilinear shape, said apparatus comprising a screen having a surface contour substantially similar to the article to be printed, supporting means for holding the article in spaced relation to the screen, an electroscopic ink-containing housing surrounding said screen, a plurality of ink dispersant particles having an overall diametral size within the range of 0.020 inch to 0.100 inch in said housing and which dispersant particles are inert with respect to the ink particles for dispersing said ink particles and for permitting the ink particles to be delivered to the screen, and means on said supporting means for jarring said housing to the extent necessary to cause ink particles to move toward the screen in an amount sufiicient to form a desired image pattern, and means operatively associated with said last named vmeans for es tablishing an electrostatic field between said supporting means and screen simultaneously with the jarring of the housing so that the ink will move toward said screen and flow through the open mesh portions of said screen to the article and thereby transfer the image pattern on said screen to the article.

13. An apparatus for electrostatically printing articles having a curvilinear shape, said apparatus comprising a screen having a surface contour substantially similar to the article to be printed, supporting means for holding the article in spaced relation to the screen, an electroscopic ink-containing housing surrounding said screen, a plurality of ink dispersant particles having an overall diametral size within the range of 0.020 inch to 0.100 inch in said housing and which dispersant particles are inert with respect to the ink particles for dispersing said ink particles and for permitting the ink particles to be delivered to the screen, ink supply means operatively mounted on said ink containing housing, means operatively associated with said ink supply housing for equally distributing charges of ink at circumferentially spaced points around said housing, and means for jarring said housing to the extent necessary to cause ink particles to move toward the screen in an amount suflicient to form a desired image pattern, and means operatively associated with said last named means for establishing an electrostatic field between said supporting means and screen simultaneously with the jarring of the housing so that the ink will move toward said screen and flow through the open mesh portions of said screen to the article and thereby transfer the image pattern on said screen to the article.

14. The process of electrostatically printing on articles having a curvilinear shape with a screen having a surface of revolution and wherein the screen has a surface coutour and shape substantially similar to the article; said method comprising positioning the screen internally in an ink feeding container, depositing ink particles among inert particles in said ink feeding container, axially shifting the article in the surface of revolution of said screen so that the axial centerline of the screen is coincident with the axial centerline of the article, establishing an electrostatic field between the screen and article and simultaneously and momentarily jarring the ink feeding container to the extent necessary to cause ink particles to move toward the screen in an amount sufficient to form a desired image pattern, feeding electroscopic ink through open mesh portions of the screen by the force of the electrostatic field and to the article thereby transferring the image pattern on said screen to the article, adding ink particles to said ink feeding container in such manner that they are distributed substantially evenly throughout, and periodically withdrawing ink particles from the bottom of said ink feeding container and at points below said screen.

References Cited by the Examiner UNITED STATES PATENTS 665,747 1/1901 Martin. 2,005,787 6/1935 Humphrey 101129 X 2,162,317 6/1939 Rez. 2,397,731 4/1946 Fowler 101129 X 2,484,671 10/ 1949 Bauman. 3,081,698 3/1963 Childress et al. 3,218,967 11/ 1965 Childress.

ROBERT E. PULFREY, Primary Examiner. E. S. BURR, Assistant Examiner. 

1. AN APPARATUS FOR ELECTROSTATICALLY PRINTING ARTICLES HAVING A CURVILINEAR SHAPE, SAID APPARATUS COMPRISING A SCREEN HAVING A CIRCUMFERENTIALLY CLOSED AND CONTINUOUS SURFACE OF REVOLUTION WITH A SURFACE CONTOUR SUBSTANTIALLY SIMILAR TO THE ARTICLE TO BE PRINTED, SUPPORTING MEANS COAXIALLY POSITIONED WITH RESPECT TO SAID SCREEN FOR HOLDING THE ARTICLE IN SPACED RELATION TO THE SCREEN, MEANS FOR COAXIALLY SHIFTING SAID SUPPORTING MEANS INTO AND OUT OF THE CONTINUOUS SURFACE OF REVOLUTION OF SAID SCREEN, INK SUPPLY MEANS FOR FEEDING ELECTROSCOPIC INK TO SAID SCREEN, AND MEANS FOR ESTABLISHING AN ELECTROSTATIC FIELD BETWEEN SAID SUPPORTING MEANS AND SCREEN SO THAT INK WILL FLOW THROUGH THE OPEN MESH PORTIONS OF SAID SCREEN TO THE ARTICLE AND THEREBY TRANSFER THE IMAGE PATTERN ON SAID SCREEN TO THE ARTICLE. 